Convert particle system wont work properly : it modifies the geometry
When the particles are converted, they aquire their size as particle, so generally much smaller than the original object.
From that, if the displacement is set to &quot;global&quot; coordinates, the mapping of the object on the voronoi texture becomes very small and so has few variations.
As solution, set the displacement to &quot;local&quot; coordinates and the mapping will be equivalent between your original objects and the converted particles.

Alternatively, you can change (lower) the voronoi texture size once the particles are converted.